Quench gasifiers are used to gasify ash containing hydrocarbon feedstocks such as residual oils, waste lubrication oils, petroleum cokes and coal. A typical quench gasifier design is shown in FIG. 1 (Reference: U.S. Pat. No. 4,828,579). The feedstock, the oxidant and a temperature moderator (either steam or carbon dioxide) are injected into the top portion of the gasifier through a burner and are mixed with one another in the reaction zone below the burner. Steam and carbon dioxide (CO2) moderate the temperatures in the reaction zone and also act as reactants. The partial oxidation reactions that take place in this portion of the gasifier, called the combustion chamber, maintain the combustion chamber temperatures in the 2000 to 3000° F. range. The combustion chamber is lined with refractory materials such as alumina. Approximately 90.0 to 99.5 percent of the carbon in the feedstock is converted to the synthesis gases (syngas).
The bottom portion of the quench gasifier, called the quench chamber, is separated from the combustion chamber by the floor of the combustion chamber as shown in FIG. 1. The combustion chamber has an internal longitudinal length L1, an external longitudinal length L2, and an internal diameter D1. A portion of the floor of the combustion chamber forms a constricted gasifier throat having an internal diameter D2. The quench chamber is partially filled with water and is not lined with refractory. The quench chamber consists of three main components: the quench ring, the dip tube and the draft tube as shown in FIG. 1. The main functions of the quench chamber are to cool down the synthesis gases generated in the combustion chamber by mixing them with water and to saturate the gases with water vapor.
The constricted gasifier throat area which directs the gases from the combustion chamber to the quench chamber is normally the coolest portion of the combustion chamber because of its distance from the gasifier burner and the burner flame. This area tends to be cooler than the rest of the combustion chamber also due to its proximity to the quench ring through which cooling water is injected into the quench chamber. As a result, the ash in the feedstock, which is in its molten or semi-molten form in the center portion of the combustion chamber, tends to solidify and form deposits or plugs in the throat area of the gasifier. These deposits are more likely to form with feedstocks that contain metal compounds such as vanadium trioxide (V2O3) because these compounds solidify at temperatures lower than 3000° F. In addition to causing shutdown of the gasifier, these compounds also react and damage the alumina type refractories that have been used in existing gasifiers (see U.S. Pat. No. 5,464,592).
A new gasifier throat design is proposed in this invention to avoid ash deposits and plugging in the throat area of the gasifier and to avoid damage to the refractories in the throat area. The proposed design will use electrical resistor heating to achieve temperatures in the range of 3000 to 3500° F. The new design will also use refractory materials like silicon carbide and silicon nitride that can withstand higher temperatures and larger temperature shocks than alumina. With this new design, it will be possible to increase the gasifier carbon conversion, reduce the steam (moderator) consumption and reduce the frequent damages that have been experienced to the refractories in the throat area of existing gasifiers. The proposed design will also decrease the capital cost of oil gasification plants by eliminating the need for soot recycle system downstream and will reduce the plant operating cost by improving the reliability of the gasifier operations.